In hepatomas induced by carcinogenic aminoazo dyes and in liver of rats treated with azocarcinogens RNA sequences which are degraded in the nucleus of normal adult liver cells are released into the cytoplasm. Our experiments indicate that the incomplete processing of newly synthesized RNA results from the interference of the azocarcinogens with the protein composition of the nuclear ribonucleoprotein particles which are involved in the processing. In the proposed experiments, we will isolate and characterize the protein in which nuclear ribonucleoprotein particles from hepatomas and from liver of rats fed with 3'-methyl-4-dimethylaminoazobenzene differ from the liver nuclear ribonucleoprotein particles of control animals. The isolated proteins will be tested for their possible enzymatic function in the processing of newly synthesized RNA. In addition in an in vitro system in which isolated hepatoma nuclei will be incubated with cytosol from hepatoma, we will try to reconstitute fully functional ribonucleoprotein particles by addition of isolated particle proteins to the system. The extent of RNA processing will be tested by competitive RNA-DNA hybridization of RNA released from the nuclei in the test systems with RNA released into the surrogate cytoplasm in an in vitro system in which nuclei from control liver will be incubated with cytoplasm from control liver cells. The proposed experiments should identify azocarcinogen-induced changes in the protein population of nuclear ribonucleoprotein particles which could lead to incomplete processing of nuclear RNA. The results of the experiments should also help us to understand the function of individual particle proteins in RNA processing and through this understanding the mechanism of the carcinogenic action of the azocarcinogens.